Field of the Invention
The invention relates to a cooling device component having a through-hole for carrying coolant, which comprises at least one heat shield made from tungsten, a tungsten alloy, a graphitic material or a carbidic material.
First wall components for fusion reactors, such as for example diverters and limiters, which are exposed to very high loads of over 10 mW/m2, are a typical example of the use of cooling device components of this type. The region exposed to the plasma is referred to as a heat shield, while the component exposed to the plasma is referred to as the PFC (plasma facing component), and the material exposed to the plasma is referred to as the PFM (plasma facing material). PFMs must be plasma-compatible, must have a high resistance to physical and chemical sputtering, must have a high melting point/sublimation point and be as resistant as possible to thermal shocks. In addition, they must also have a high thermal conductivity, a low neutron activation and sufficient strength/fracture toughness, combined with good availability and acceptable costs. Tungsten, tungsten alloys (e.g. W-1 wt. % La2O3), graphitic materials (e.g. fiber-reinforced graphite) and carbidic materials (e.g. boron carbide) best satisfy this multi-faceted and in some cases contradictory profile of requirements. Since the energy flows act on these components for a prolonged period of time, cooling device components of this type are typically actively cooled. The dissipation of heat is assisted by heat sinks, for example made from copper or copper alloys, which are usually connected to the PFM.
Cooling device components can have various designs. In this context, a distinction is drawn between plane tile, saddle and monobloc design.
If a PFM tile with a planar connection surface is joined to the heat sink through which the coolant flows, this is referred to as a plane tile design. In the saddle design, a PFM body with a semicircular recess is joined to a tubular heat sink. The heat sink in this case has the function of producing the thermal contact between the heat-introduction side and the cooling medium and is exposed to cyclic, thermally induced loads resulting from the temperature gradient and the different expansion coefficients of the joining partners.
In the monobloc design, a pipe carrying cooling water is surrounded by the PFM heat shield which has a closed through-hole. Whereas in the saddle and plane tile design, individual heat shield components can become detached from the heat sink on account of the cyclic, thermo-mechanical loading in use, the monobloc design precludes the loss of heat shield components for geometric reasons. However, the drawback of the monobloc design is that the PFM has to cope not just with thermally induced loads but also with additional mechanical loads. Additional mechanical loads of this nature can be produced by electromagnetically induced currents which flow in the components and interact with the surrounding magnetic field. This can give rise to high-frequency acceleration forces which have to be transmitted by the structures involved. In the plane tile and saddle design, these forces are transmitted via structural materials, but in the monobloc design they are transmitted by the PFM. However, tungsten, tungsten alloys, graphitic and carbidic materials have
a low fracture toughness. An additional factor in the case of fiber-reinforced graphites is the relatively low strength. In addition, neutron embrittlement occurs in use, resulting in a further increase in the susceptibility of these materials to incipient cracking. Despite many years of expensive development work in the field of first wall components, the parts which are currently available do not optimally satisfy this profile of demands. This is one reason why large-scale industrial implementation of fusion technology remains far from imminent.